The present invention relates to elemental analyzers, and more particularly elemental analyzers for combusting a sample into constituent gases for subsequent analysis.
The determination of the carbon, hydrogen, and nitrogen content of an organic material is necessary to a variety of determinations, such as the potential heat content of the material, as is particularly useful in evaluating coal and coke. Second, the elemental content is essential in the elemental analysis of the material as well as in determining the carbon-to-hydrogen ratio. Third, the elemental content provides an indication of the purity of an organic compound, for example graphite. Fourth, the nitrogen content of an organic is helpful in evaluating the material's potential for producing polluting nitrogen oxide.
The ASTM Standards for determining the carbon, hydrogen, and nitrogen content of an organic material are complicated and time consuming. The carbon and hydrogen are measured by burning a weighed quantity of the sample in a flow thru system and then fixing the products of combustion in an absorption train after oxidation and purification to measure the carbon dioxide and water produced. Nitrogen content is determined by converting the nitrogen to ammonium salts, decomposing the salts, distilling the resultant ammonia, and titrating the ammonia.
Although analyzers have been developed for analyzing the carbon, hydrogen, and nitrogen content of a material, these analyzers are not without their drawbacks. The analyzers typically combust the sample into constituent gases and then analyze the gases to calculate the elemental content. However, these machines usually require that the entire volume of gas produced during combustion be reduced to eliminate nitrogen oxides prior to the nitrogen measurement with a thermal conductivity cell. All carbon dioxide and water vapor must also be removed from the gas stream prior to the nitrogen measurement. Consequently, these analyzers must analyze only small samples to prevent the reducing agents and absorbers from becoming rapidly fouled. However, small samples lead to relatively large measurement errors. If the sample size is increased, the reducing agents and absorbers must be replaced relatively frequently.
Second, known machines typically provide a fixed combustion period to allow for complete sample destruction. However, when working with materials which combust relatively rapidly, the fixed combustion period is excessively long, resulting in excessively long analysis times. Although detection cells have been employed to monitor the combustion products to determine when combustion is essentially complete, the inclusion of these cells in an analyzer increases the cost and complexity of same.
Third, although some machines introduce oxygen into the furnace chamber during combustion to increase the rate at which the sample combusts, the oxygen is consumed relatively rapidly in the immediate area of combustion. Although a great deal of oxygen is generally available in the furnace, the oxygen concentration in the combustion area is relatively low.
Fourth, known analyzers typically provide a generally horizontally oriented combustion chamber communicating and aligned with a generally horizontally oriented reduction chamber. Therefore, gravity feed may not be utilized in dropping samples into the combustion chamber. Further, the aligned combustion chamber and reagent chamber require excessive horizontal space.